Use of stannane as a reducing agent

ABSTRACT

The method of this invention for reducing organic substrates comprises reacting as reactants stannane, SnH4, and an organic substrate, maintaining said reactants together in a reaction mixture, and separating said reduced substrate from said reaction mixture.

United States Patent [191 Reifenberg et al.

[451 Feb. 18 1975" 1 USE OF STANNANE AS A REDUCING AGENT [75] Inventors: Gerald H. Reifenberg, l-lightstown;

William J. Considine, Somerset,

[211 App]. N0.: 255,198

Related US. Application Data [62] Division of Ser. No. 59,839, June 24, 1970, Pat. No. 3,708,549, which is a division of Ser. No. 742,164, Jan. 3, 1968, Pat. No. 3,654,367.

52 us. Cl. 260/618 n, 260/638 B [51] im. 01 C07c 29/14 581 Field Of Search 260/617 c, 618 CF, 638 B [56] References Cited UNITED STATES PATENTS Schlesinger et a1. 260/347.8 X

OTHER PUBLlCATlONS Chemical Abstracts, Vol. 69 (1968) 51345y. J.A.C.S.Vo1. 83 No. 5 (1961) 12461250.

T. Moeller, Inorganic Chemistry Willey, 1952, pp.

S. Patai The Chemistry of the Carboxyl Group Interscience (1966) pp. 541553.

Primary Examiner-Donald G. Daus Assistant Examiner-D. B. Springer Attorney, Agent, or Firm-Robert P. Auber; Kenneth G. Wheeless; Robert Spector 157] ABSTRACT The method of this invention for reducing organic substrates comprises "reacting as reactants stannane, SnH and an organic substrate, maintaining said reactants together in a reaction mixture, and separating said reduced substrate from said reaction mixture.

1 Claim, N0 Drawings USE OF STANNANE AS A REDUCING AGENT This application is a divisional application of Ser. No. 59,839, filed June 24, l970, now US. Pat. No. 3,708,549, issued Jan. 2, 1973, which is in turn a divisional application of Ser. No. 742,164, filed July 3, 1968, now US. Pat. No. 3,654,367, issued Apr. 4, 1972.

This invention relates to a novel method for reducing organic substrates. More specifically this invention relates to a process for preparing alcohols, amines, and hydrocarbons. The method of this invention for reducing organic substrates comprises reacting as reactants stannane, Snl-l and an organic substrate, maintaining said reactants together in a reaction mixture, and separating said reduced substrate from said reaction mixture.

The method of this invention for reducing organic substrates comprises reacting as reactants stannane, Snl-h, and a compound of the formula i R-A-Y in which A is selected from the group consisting of carbon and nitrogen, Z and Y are selected from the group consisting of oxygen, halogen, hydrogen, and R such that only one of Z and Y is R or hydrogen, wherein R and R are hydrocarbon radicals free of olef'mic and acetylenic unsaturation, selected from the group consisting of alkyl, alkaryl, aralkyl, aryl, and cycloalkyl, maintaining said reactants together in a reaction mixture, and separating said reduced organic substrates from said reaction mixture.

According to another of its aspects, the method of this invention for preparing alcohols, amines, and hy-. drocarbons comprises reacting as reactants tin tetrahalide in the presence of a lithium aluminum hydride reducing agent to produce stannane, Snl-l reacting as reactants said stannane, SnH and a compound in which A is selected from the group consisting of carbon and nitrogen, Z and Y are selected from thegroup consisting of oxygen, halogen, hydrogen and R such that only one of Z and Y is R" or hydrogen wherein R and R are hydrocarbon radicals free of olefinic and acetylenic unsaturation selected from the group consisting of alkyl, alkaryl, aralkyl, aryl, and cycloalkyl, maintaining said reactants together in a reaction mixture, and separating said reduced organic substrates from said reaction mixture.

According to one of its aspects, the method of this invention for preparing alcohols, ROH, comprises reacting as reactantsstannane, SnH and a compound selected from aldehydes and ketones of the formula wherein Z is selected from the group consisting of hydrogen and R, wherein R and R are hydrocarbon radicals free of olefinic unsaturation selected from the 2 group consisting of alkyl, alkaryl, aralkyl, aryl, and cycloalkyl radicals, maintaining said reactants together in a reaction mixture, and separating the alcohol from said reaction mixture.

In accordance with another of its more circumscribed aspects, the method of this invention for preparing organic amines, RNH- comprises reacting as reactants stannane, Snl-l and a compound of the formula RNO wherein R is a hydrocarbon radical, free of olefinic and acetylenic unsaturation, selected from the group consisting of alkyl, alkaryl, aralkyl, aryl, and cycloalkyl radicals, maintaining said reactants together in a reaction mixture, and separating RN H from said reaction mixture.

Another aspect of the method for this invention for preparing. hydrocarbons, RH comprises reacting as reactants stannane, Snl-l and a compound of theformula RX wherein X is a halogen selected from the group consisting of chlorine, bromine and iodine and R is a hydrocarbon radical, free of olefinic and acetylenic unsaturation, selected from the group consisting of alkyl, alkaryl, aralkyl, aryl, and cycloalkyl radicals, maintaining said reactants together in a reaction mixture, and separating RH from said reaction mixture.

In the foregoing compounds R and R may each be a hydrocarbon radical preferably selected from the group consisting of alkyl, cycloalkyl, aralkyl, aryl, alkaryl, including such radicals when inertly substituted. When R or R is alkyl, it-may typically be straight chain alkyl or branched alkyl, including methyl, ethyl, npropyl, isopropyl, n-butyl, isobutyl, sec-butyl, tertbutyl, n-amyl, neopentyl, isoamyl, n-hexyl, isohexyl, heptyls, octyls, d ecyls, dodecyls, tetradecyl, octadecyl, etc. Preferred alkyl includes lower alkyl, i.e., having less than about eight carbon atoms, i.e., octyls and lower. When R is cycloalkyl, it may typically be cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, etc. When R is aralkyl, it may typically be benzyl, B-phenylethyl, 'y-phenylpropyl, B-phenylpropyl, etc. When R is aryl, it may typically be phenyl, etc. When R is alkaryl, it may typically be tolyl, xylyl, p-ethylphenyl, p-nonylphenyl. etc. R may be inertly substituted, e.g. may bear a nonreactive substituent such as alkyl, aryl, cycloalkyl, aralkyl, alkaryl, alkenyl, ether, ester, etc. Typical substituted alkyls include 2-ethoxyethyl, carboethoxymethyl, etc. Substituted cycloalkyls include 4- methylcyclohexyl, etc. lnertly substituted aryl includes anisyl, biphenyl, etc. lnertly substituted aralkyl includes p-phenylbenzyl, pmethylbenzyl, etc.

This invention comprises the reduction of organic compounds by reactively contacting said compounds with stannane, Snl-l and recovering said compounds in their reduced state. Illustrative reactions include those in which ketones, aldehydes, nitro compounds, alkyl halides, aryl halides, cycloalkyl halides, and organometallic halides are reduced. Acetone when reacted with stannane, SnH is reduced to isopropyl alcohol; benz-.

aldehyde-is reduced to benzyl alcohol; nitrobenzene is functional group to be reduced should be at least 0.5

when ketones or aldehydes areto be reduced; at least 1.5 when nitro functional groups are to be reduced; and

at least 0.25 when halogen groups are to be reduced.

Stannane, SnH may be prepared by reacting tin tetrachloride, tin tetrabromide or tin tetraiodide with lithium aluminum hydride in the presence of a nitrogen atmosphere containing about 0.1% oxygen. The reactions of this invention are preferably carried out under inert atmosphere, e.g. nitrogen containing approximately 0.1%, by weight, oxygen since stannane, SnH is relatively unstable. In preparing stannane, Snl-l by the reduction of tin tetrahalide, the tin tetrahalide may be reacted with lithium aluminum hydride at a temperature ranging from 200 C to 20 C. The temperature, initially. is preferably near 200 C and is preferably elevated slowly to 70 C to avoid decomposing stannane. It is noted that the melting point of stannane, Snl-h, is l46 C and the boiling'point is 52.5 C.

In reducing tin tetrahalide to stannane, the molar ratio of lithium aluminum hydride to tin tetrahalide should be greater than unity, preferably 2 or 3 to 1.

During the preparation of stannane the following typical reaction may occur: SnCl, LiAlH, SnH,

LiAlCl, I

In practice of the process of this invention, the reactantsare mixedtogether to form the reaction mixture. It may be; desirable to usein the reaction mixture an inert diluent. Solvents or diluents suitable as the reaction medium of this invention include aliphatic hydrocarbons, aromatic hydrocarbons and ethers. The fore-.

going may contain carboxylic esters, carboxylic amides, and nitrile groups as substituents. Aromatic amino groups, but not aliphatic amino groups, may also ,be present as substituents. Among the suitable solvents are diethyl ether and tetrahydrofuran. The substrate to be reduced, e.g. benzaldehyde, is charged into a reaction vessel or trap that may be preferably immersed in liquid nitrogen, the liquid nitrogen exhibiting a temperature of approximately l95 C. Stannane, Snl-l.,, is then added to the reaction vessel or trap, after which the temperature may be adjusted slowly and incrementally, to room temperature, approximately 20 C. The reaction temperature may be adjusted to a higher temperature,circa. 78 C, by transferring the reaction vessel or trap, from the liquid nitrogen bath .(at 195 C) to a dry ice-acetone bath at approximately 78 C; and thereafter, to an ice-methanol bathat -22 C. After removing the reaction mixture from the ice-methanol bath the temperature may be allowed to rise to room temperature. Unreacted stannane, SnH may be collected in conventional traps outside the reaction zone. The reaction mass may be filtered to separate the product.

Practice of this invention may be observed from the following illustrative examples.

EXAMPLE 1 The reactants 6.5 grams (0.025 mole) of tin tetrachloride and 4.8 grams (0.125 mole) of'lithium alumicontaining 0.1% oxygen. The temperature of the reaction vessel was slowly increased and at 62". C ebullition of gas was observed. The temperature,thereafter,

was slowly and incrementally increased toroom tem- 5 perature, 27 C, whereupon the stannane, SnH product was collected in traps. The stannane product exhibited a weight of 2.85 grams (0.023 mole) and an 87.2%

yield. e

To a vessel or trap, immersed in an ice-water bath (0 C) was added 51.2 grams (0.48 mole) of benzaldehyde. Stannane 2.85 grams (0.023 mole) at l95 C from an adjoining, connected trap was'slowly bubbled through the benzaldehydeduring a 150 minute time interval. At the termination of the reaction period, the resultingmixture was filtered to remove tin metal. The product, benzyl alcohol, exhibited a weight of 2.82 grams. The identification of the product was confirmed by vapor phase chromatographic analysis. v

EXAMPLE 2 The preparation of isopropyl alcohol from'acetone.

The procedure of Example 1 was followed except that the reaction vessel was charged with 2.75 grams of stannane, Snl-l and 21.7 grams of acetone.The product, isopropyl alcohol, exhibited a weight of.l .0] grams (0.017 mole). The identification of the product was confirmed by vapor phase chromatographic analysis.

EXAMPLE 3 The preparation of isopropylamine from 2- nitropropane.

The procedure of Example 1 was followed except that the reaction vessel was charged with 2.7 grams of stannane, SnH and 26.0 grams (0.29 mole) of 2- nitropropane. I

The reaction trap was in a liquid nitrogen bath, exhibiting a temperature of l95 C. The temperature of the reaction mass was then adjusted by sequentially transferring the reaction vessel from the liquid nitrogen bath at l95 C to a dry ice-acetone bath exhibiting a temperature of approximately .-78 C andthen, to an ice-methanol bath at 22 C. The temperature of the reaction vessel was then allowed to rise to room tem' perature (26 C). 4

The total time period for the sequential temperature increases to be effected was 3.5 hours.The product, isopropylamine, exhibited a weight of 0.14 grams.

EXAMPLE 4 The preparation of aniline from nitrobenzene.

The procedure 'of Example 1 was followed except that the reaction vessel was charged with 2.65 grams (0.025 mole) of stannane, SnH and 44.5 grams (0.36 mole) of nitrobenzene. The product, aniline, exhibited a weight of 0.31 grams. The identification of the product was confirmed by vapor phase chromatographic analysis.

EXAMPLE '5 The preparation of toluene from benzyl chloride. The procedure .of Example 3 was followed except that the reaction vessel was charged with 2.9 grams of ride. The product, toluene, exhibited a weight of 3.0 grams. The identity of the product was confirmed by vapor phase chromatographic analysis.

stannane, and 38.0 grams (0.3 mole) of benzyl chlosaid method comprising the step of reacting acetone or benzaldehyde with stannane, SnH maintaining the reactants together in a reaction mixture wherein the temperature is maintained at about -l C., and subsequently separating the resultant alcohol from the reaction mixture. 

1. A METHOD FOR REDUCING ACETONE OR BENZALDEHYDE TO FORM ISOPROPANOL OR BENZYL ALCOHOL, RESPECTIVELY, SAID METHOD COMPRISING THE STEP OF REACTING ACETONE OR BENZALDEHYDE WITH STANNANE, SNH4, MAINTAINING THE REACTANTS TOGETHER IN A REACTION MIXTURE WHEREIN THE TEMPERATURE IS MAINTAINED AT ABOUT -195*C., AND SUBSEQUENTLY SEPARATING THE RESULTANT ALCOHOL FROM THE REACTION MIXTURE. 